This invention relates to rotating pumps or compressors of the scroll type, and is more particularly directed to a scroll type compressor having an improved high-pressure port at the center of one of the scrolls.
Scroll type compressors have been known, in principle, for several decades. In general, a scroll-type compressor or similar machine comprises a pair of mating scrolls, which have involute spiral wraps of similar shape, mounted on respective base plates. Normally, one scroll is held fixed, and the other is orbited to revolve, but not rotate, being held by an Oldham ring or other anti-rotating structure. In some versions both scrolls rotate synchronously on eccentric shafts. The walls of the two involute wraps define crescent-shaped volumes which become smaller and smaller and move from the outside to the center of the mating scrolls as the orbiting scroll revolves. A compressible fluid, such as a refrigerant gas, can be introduced at the periphery of the spiral wraps, and is compressed as it is moved under the orbiting motion of the device. The compressed fluid is then discharged through an opening or port at the center. By introducing a compressed fluid at the center and permitting its expansion to drive the device, the scroll machine can be used as a motor.
In a conventional scroll compressor, the discharge port, which is machined through the stationary scroll, is circular in shape and is limited in diameter by the geometry of the scroll itself. The small-size discharge port can act as an orifice or restriction and reduce output pressure due to its resistance to fluid flow. One attempt to increase the discharge port diameter is described in U.S. Pat. No. 4,498,852, an oversize hole is bored through the fixed scroll at its center. That hole has to be machined in from the back, i.e., the side opposite the wrap. Consequently, manufacture involves additional manufacturing steps of inverting and accurately positioning the scroll. Because the oversize hole is bored partly into the spiral wrap, the wrap wall is weakened at the center, where gas pressure is highest. Also, the thin remaining wrap wall at this point leaves only a small margin for machining error. This fact, coupled with the problems inherent in drilling through from the back, can lead to a significant scrap rate for this design.